THE RAFFLES BULLETIN OF ZOOLOGY1998 46(2): 627-650© National University of Singapore

FRESHWATERCRABS OF THE POTAMON TANNANTI SPECIESGROUP (CRUSTACEA: DECAPODA: BRACHYURA:POTAMIDAE) FROM NORTHERN INDOCHINA
Darren C. J. Yeo and Peter K. L. Ng
Departmentof Biqlogical

Sciences, National University of Singapore,
Singapore 119260, Republic of Singapore

10 Kent Ridge Crescent,

ABSTRACT. - Several species of potamid crabs with aquatic habits have been confusedwith Potamon tannanti Rathbun, 1904. The present study separates P. tannanti s. str.,from these congeners, some of which occur in the southern Chinese province of Yunnan
as well, by using carapace, gonopodal and male tel son characters. Potamon tannanti
is redescribed; P. orleansi Rathbun, 1904, a species previously synonymised under P.
tannanti is resurrected; and four new species are described, viz., P. eua, new species,
P. guttus, new species, P. ou, new species, and P. villosum, new species. An artificial
key to these species is included.

Freshwater potamid crab species are medically important in northern Vietnam (and probably
northern Laos as well) due to their role as intermediate hosts to the parasitic lung fluke,
Paragonimus, being an important component in the diet of rural and hill tribes (V. D. Nguyen,pers. comm.). It is known that crabs from certain localities show relatively lower infection
rates, indicating possible species specificity in infection (V. D. Nguyen, pers. comm.). It isthus critical to be able to properly identify the various crab species.
In this paper, Indochina is defined as consisting of Vietnam, Laos and Cambodia (historicalFrench-Indochina), with northern Indochina referring to northern Vietnam and northern Laos.
We have followed Dang & Tran (1992) in regarding Thanh Hoa Province as part of central
Vietnam, as such, the provinces north of Thanh Hoa Province constitute northern Vietnam.
In the case of Laos, we have regarded Khammouan Province as part of central Laos and theregions north of it are defined herein as northern Laos.

The most recent studies on Vietnamese freshwater crabs were by Dang (1975, 1980), in
which seven species of Potamidae were recognized from northern Vietnam (= Tonkin),
namely, Potamiscus
tannanti (Rathbun,
1904), P. cucphuongensis
Dang, 1975,
Tiwaripotamon annamense (Balss, 1914), Orientalia glabra (Dang, 1967), Ranguna(Ranguna) fruhstorferi (Balss, 1914), Ranguna (Ranguna) luangprabangensis (Rathbun,
1904), and Ranguna (Ranguna) kimboiensis Dang, 1975. Of these, only P. tannanti will be
dealt with in the present paper. Rathbun (1904) had described another species, Potamon
orleansi, from the Song Da river (= riviere Noire, Tonkin) which was synonymised by Bott
(1966, 1970) under Potamiscus tannanti, an action which Dang (1975, 1980) followed.
Another taxon, Potamon luangprabangensis mieni Dang, 1967 [Son La Province], was also
subsequently synonymised under P. tannanti by Dang (1975, 1980). As a result, a numberof medium to large-sized, aquatic, pot amid crabs found in northern Laos and Vietnam, havebeen referred to P. td~nanti (see Bott 1966, 1970; Dang 1975, 1980). The present study,
however, has revealed that these specimens are actually several closely related species
distributed throughout northern Indochina and southern China, which include P. tannanti
Rathbun, 1904 s. str. [northern Vietnam, southern China]; P. orleansi Rathbun, 1904 [northern
Vietnam]; P. mieni Dang, 1967 [northern Vietnam]; P. jinpingense Dai, 1995 [northern
Vietnam, southern China]; and four previously undescribed species. These differ in somekey carapace, gonopodal and male tel son characters. The present paper clarifies the identitiesof these members of P. tannanti species group.
The following abbreviations are used: G 1 for male first pleopod, G2 for male second pleopod.
Measurements are of carapace width and length respectively. Terminology used essentiallyfollows Ng (1988). All measurements are in millimetres. Specimens are deposited in thethe Zoological Reference Collection (ZRC) of the Raffles Museum, National University ofSingapore; Museum National d'Histoire Naturelle (MNHN), Paris, France; and Chulalongkorn
University Natural History Museum (CUMZ), Bangkok, Thailand. A full description is
given only for Potamon tannanti, while diagnoses are given for the other species.

Potamon Savigny,6.

1816: 251; Alcock 1910: 18; Naiyanetr & Ng 1990: 121; Ng & Naiyanetr 1993:

Remarks. - Alcock's (1910) generic classification of the Potamidae (as Potamonidae), in
which Potamon is distinguished by the presence of a well-developed flagellum (as opposedto vestigial or absent) on the third maxilliped exopod, is followed here (see also Naiyanetr& Ng 1990; Ng & Naiyanetr 1993). All the species in the present paper have well-developed
third maxilliped flagella and thus have been assigned to Potamon sensu lato, pending a revisionof the genus Potamon s. str.
The Potamon tannanti species group is a utilitarian grouping based on habits and morphology,
and does not necessarily imply phylogenetic closeness. The members ofthis group recognizedfrom northern Indochina are medium to large-sized, aquatic, Potamon species found in flowing
streams, namely, P. tannanti, P. orleansi, P. mieni, P. jinpingense, P. cua, new species, P.

guttus, new species, P. ou, new species, and P. villosum, new species (present study). A
ninth member of this species group, Potamon lipkei Ng & Naiyanetr, 1993, is found in northern
Thailand, and was also previously misidentified as P. tannanti (see Ng & Naiyanetr 1993:
19). It is easily separated from the other group members as its G I terminal segment isdistinctly more strongly bent than any of the present Indochinese species (cf. Ng & Naiyanetr,
1993: Fig. 47). The Potamon tannanti species group is characterized by a combination ofdiagnostic morphological characters: i) low, relatively flat, broader than long carapace, withrugose epigastric cristae separated from postorbital cristae by distinct groove, and postorbitalcristae breaking up into granules or rugae just before the epibranchial tooth; ii) serrated,distinctly cristate, convex anterolateral margins and gently convergent posterolateral margins;iii) granulose to rugose branchial region and regions behind epigastric and postorbital cristae;iv) rectangular, elongated '(about twice as long as merus) third maxilliped ischium, withlong exopod, bearing1well-developed flagellum not exceeding width of merus; v) relatively
stout ambulatory legs; vi) triangular male abdomen, with very gently to distinctly concave
telson lateral margins; vii) relatively straight, stout, conical to sub-cylindrical G 1 terminal
segment, without dorsal flap, with groove for G2 marginal on inner (upper) side; viii) andG2 with distal segment greater than half length of basal segment.
Members of the Potamon tannanti species group differ from the six other potamid species
reported by Dang (1980) significantly in external morphology as well as in male first pleopod
structure (cf. above). The squarish carapace of Potamiscus cucphuongensis, smooth, confluent
epigastric and postorbital cristae of Ranguna (Ranguna) fruhstorferi, and smooth, swollen
carapace of Orientalia glahra immediately separate these species from the P. tannanti species
group (cf. Bott 1970: PI. 49 fig. 40; Dang 1980: Figs. 242, 247). Long, slender ambulatory
legs of Tiwaripotamon annamense prevent it from being confused with P. tannanti species
group members as well (cf. Bott 1970: PI. 53 fig. 61). Ranguna (Rang una) luangprahangensis
and R. (R.) kimhoiensis do superficially resemble Potamon tannanti species group members
but the general shape of their G 1 terminal segments (slender, strongly curved) and presenceof a distinct dorsal flap in the G 1 terminal segment also necessitates the exclusion of these
two species from the grouping (ef. Bott 1970: PI. 37 fig. 6, PI. 48 fig. 35; Dang 1980: Fig.
245).

Potamon tannanti Rathbun, 1904
(Figs. 1, 2A-G , 6A)
Potamon (Potamon) tannanti Rathbun, 1904: 279, Fig. 17, PI. 11 fig. 8.
Potamiscus (Potamiscus) tannanti - Bott 1966: 480 (part).
Potamiscus tannanti - Bott 1970: 160, ?Pl. 47 fig. 28 (part); Dang 1975: 75,1980: 432 (part).
Potamon hokuoense Dai, Song, He, Cao, Xu & Zhong, 1975: 258, PI. 2 fig.2, Fig.2.

Material examined. - Holotype, female (35.5 by 27.7 mm)(MNHN-B 5313), "Tonkin, montagnes du
Yunnan (via Lao Koi)", colI. Tannant, no date. Others - 1 male (56.1 by 42.6 mm)(ZRC 1998.264),
Hekou, Yunnan Province, southern China, coIl. A.-Y. Dai., 29 Nov.1995.

Description of male (ZRC 1998.264). - Carapace broader than long, low; dorsal surface
relatively flat; glabrous to very sparsely setose along outer edge of metabranchial region,
with very short, indistinct setae, gently convex laterally; strongly sculptured in appearance,with regions well-defined, cervical grooves deep, distinct, expanded anteriorly, reachinglateral end of postorbital cristae, H-shaped depression distinct (Figs. lA, IB). Epigastriccristae well-developed, not sharp, rugose, separated by distinct groove which opens up into

inverted V -shape posteriorly, in line with but separated from postorbital cristae by short but
distinct groove; postorbital cristae strongly developed, relatively sharp, weakly cristate, gently
sloping posterolaterally before breaking up into granules just before epibranchial tooth; regions
behind epigastric and postorbital cristae with weak rugae and granules (Figs. lA, IB). Frontal
margin gently sinuous, gently emarginate medially; frontal region gently deflexed downwards,
appearing relatively broad in dorsal view, weakly granular; supra- and infraorbital margins
almost straight, weakly cristate; orbital region smooth, relatively broad, slightly expanded
laterally; eyes normal; subhepatic and subbranchial regions slightly rugose (Figs. lA, IB).
External orbital angle triangular, outer margin almost straight, distinctly cristate; epibranchial
tooth low but distinct, triangular, separated from external orbital angle by distinct cleft, left
epibranchial tooth previously damaged, replaced with anteriormost serration of anterolateral
margin produced as s1llflll,acute tooth; anterolateral margin convex, weakly serrated, distinctly
cristate; posterolateral margin entire, almost straight, not strongly convergent posteriorly;
branchial region granulose to very slightly rugose; metabranchial region lined with few,
faint oblique striae (Fig. 1A). Epistome anterior margin with median triangle; posterior
margin with median triangular tooth (Fig. lB).
Ischium of third maxilliped rectangular, about 1.5 times longer than broad, with distinct,
well-developed, longitudinal median sulcus; merus squarish, subequal to half of ischium
length, with concave outer surface; palp normal; exopod long, exceeding upper edge ofischium but not reaching midpoint of merus, inner margin of distal part produced as a blunt
tooth, with well-developed flagellum not exceeding width of merus (Fig. 1B)(see also Fig.
2A).
Chelipeds subequal; outer surface of palm sparsely covered with rounded, flattened, forwarddirected granules to weakly rugose, fingers gaping, shorter than palm, tips overlapping, withseveral longitudinal rows of pits, movable finger with two rows of forward-directed, sharp
granules; carpus with rugose outer surface, granular along outer surface of inner margin,
with robust, obliquely directed, subdistal spine on inner margin, with anterior part of outermargin entire; merus with serrated edges, without subterminal spine (Fig. lA).
Ambulatory legs glabrous; second pair longest, dactylus long, slender, about 1.1 times aslong as propodus, about 7 times longer than proximal width, with low, barely visible medianridge, propodus with broad ridge, carpus with sharply defined ridge, merus weakly rugose,with distinctly serrated upper margins, without subdistal spine; fourth ambulatory leg merussmooth, with upper margins entire (Fig. I A).
Suture between sternites 2 and 3 complete, distinct, gently emarginate medially; suture
between sternites 3 and 4 discernible only by notches at lateral edges of sternum (Fig. IC).
Male abdominal cavity reaching imaginary line joining median points of cheliped bases(Fig. IC). Male abdomen triangular; tel son longer than sixth segment, lateral margins very
gently concave, tip rounded; segment 6 with median length slightly more than half of proximal
margin length, lateral margins distinctly convex; lateral margins of segments 4 to 5 straight;
lateral margins of segment 3 gently convex (Figs. I C, 2D).
G I broad; terminal segment clearly separated from subterminal segment, about 0.4 times
length of subterminal segment, slender, about 3.6 times longer than broad, without dorsal
flap, conical, tip almost straight, not "bottle-neck" -like, without distinct narrowing towards
tip, with distinct ventral distal opening; subterminal segment broad, without neck-like distal
part, without subdistal cleft on outer margin, without distinct rounded distal protuberance

Fig. I. Potamon tannanti Rathbun,
B: frontal view; C: ventral view.

1904, male (56.1 by 42.6 mm)(ZRC 1998.264). A: dorsal view;

on outer margin (Figs. 2B-C, E-F). G2 with distal segment greater than half length of basal
segment (Fig. 2G).
Remarks. - Only one specimen, a female (MNHN-B 5313)(35.5 by 27.7 mm), was examinedby Rathbun (1904) in her original description of Potamon tannanti. This specimen (effectively
the holotype) was collected from "Tonkin, montagnes du Yunnan (via Lao Koi)", whichmost probably refers to the present day area around Hekou in Yunnan Province of southern
China - Hekou being a border town immediately opposite the Vietnamese border town of
Lao Cai. Hekou is also the type locality of Potamon hokuoense Dai, Song, He, Cao, Xu &Zhong, 1975. "Hokuoense" was used as the specific epithet by Dai et al. (1975) instead of"hekouense" as the pronunciation of the local dialect of that region was followed (Y. -X.
Cai, pers. comm.). The topotypic male specimen (ZRC 1998.264)(56.1 by 42.6 mm) from
Hekou examined in the present study, was originally determined by Prof. Dai Aiyun as
Potamon hokuoense, but is identical to the holotype in most external characters, with someminor exceptions (see next paragraph). We are thus confident that the two specimens are
con specific and that P. hokuoense is, in fact, a junior synonym of P. tannanti Rathbun,
1904.
The redescription of the present species has been based on the male specimen (ZRC 1998.264)
from China as it possesses the taxonomically important Gis and it is also larger (56.1 by
42.6 mm). The female holotype (MNHN-B 5313), although fully adult (as evident by the
fully expanded abdomen), is rather small (35.5 by 27.7 mm) and may not clearly exhibit
some of the important external taxonomic characters. The external asexual characters of theholotype are almost identical to the male, with the following exceptions, which may be sizerelated, viz., i) posterolateral margins being gently converging distally (versus more distinctly
converging posteriorly); ii) external orbital angle outer margin being slightly convex (versus
almost straight); and iii) dactylus of second ambulatory leg about 1.2 times propodus length(versus 1.1 times). These slight differences, however, are not regarded as specificallyimportant.
The material examined by Bott (1966, 1970)(all from MNHN) under Potamiscus tannanti
included one male from "Yiinnanberge, chines. Grenze; Hanoi", three males and one juvenile
female from "Ban-Nong, ober Laos", and one male he identified as P. orleansi Rathbun,
1904, from "Schwarzer Fliiss bei Hanoi, Tonkin", which was then regarded as a juniorsynonym of P. tannanti. No indication was given as to whether the holotype of either species
had been examined (Bott 1966, 1970). In any case, the Gis figured in Bott (1966: Fig. 14;
1970: PI. 38 fig. 30) definitely do not belong to P. tannanti as presently defined, and it isactually a distinct species from P. tannanti (present study). Unfortunately, we have only
been able to obtain for study, two of the three male specimens from Laos that Bott (1966)
examined. These have different G I structures from P. tannanti, and have been assigned toa new species, P. guttus (see later). It is important, however, that the remaining specimensthat Bott (1966, 1970) listed be found and reexamined, to clarify their identities. Bott's(1970: PI. 47 fig. 28) photograph of P. tannanti, for which the size measurements of 57 by
45 mm, and locality of "Hanoi, Tonkin" were given, could refer to the single male from
"Yiinnanberge, chines. Grenze; Hanoi". However, we cannot be certain. The triangulartelson with straight lateral margins (see Bott 1970: PI. 47 fig. 28) seems to indicate that the
specimen might be P. tannanti, but the G I (see Bott 1970: PI. 38 fig. 30) appears more likethat of P. guttus (see later), which raises the possibility that the figures in the two plates
were from two different specimens.

Dang (1975, 1980) followed Bott's actions exactly in regarding P. orleansi as a juniorsynonym of P. tannanti, to the point of reproducing
Bott's (1970) figures of P. tannanti (seeDang 1980: Fig. 246).
Dang (1975)
also synonymised
anothertaxon, Potamon
luangprabangensis mieni Dang, 1967, under P. tannanti. This species is also resurrected in
the present study (see later). No "material examined"
was given for P. tannanti by Dang
(1975, 1980).

Potamon tannanti is closest
differences
betweenTables 1, 2).

to Potamon cua, new species, from northern Vietnam. The
the two species are in the branchial region, male tel son and G 1 (seeDistribution.
Tonkin,- Hekou, Yu'lman Province, southern China (Dai et al. 1975; present study);
montagnes
Yunnan (via Lao Koi)", northern Vietnam (Rathbun 1904).

dh

Table I. Main difference
Indochina (I).

betweenmembersof the Potamon

tannanti species group of northern

Character

Carapace

Anterolateral
marginBranchial region

Male tel son

P. tannanti

Very sparsely
setose, regions
well-defined.

Weakly serrated,cristate.

Granulose to veryslightly rugose.

Triangular, withvery gently
concave lateral
margins.

P.orleansi

Glabrous, regions
not well-defined.

Weakly serrated,cristate.

Weakly rugose.

Triangular, with
distinctly concave
lateral margins.

P. mieni

Glabrous, regions
not well-defined.

Weakly serrated,cristate.

Weakly rugose.

Narrowly
triangular, with
distinctly concave
lateral margins.

P. jinpingense

Glabrous, regions
not well-defined.

Serrated, cristate.

Weakly rugose.

Narrowly
triangular, with
distinctly concave
lateral margins.

P. cuaSparsely setose,regions welldefined.

Weakly serrated,cristate.

Distinctly rugose.

Triangular, withslightly concave
lateral margins.

P. guttus

Glabrous, regions
well-defined.

Distinctly serrated, Distinctly rugose.
cristate.

Triangular, withslightly concave
lateral margins.

P.ou

Glabrous, regions
not well-defined.

Distinctly serrated, Rugose.
strongly cristate.

Narrowly
triangular, with
distinctly concave
lateral margins.

P. villosum

Distinctly setose,regions not
well-defined.

Distinctly serrated, Distinctly rugose.
strongly cristate.

Narrowly
triangular, with
distinctly concave
lateral margins.

G I terminal segment

G I subterminal

Slender, about 3.6 times longer thanbroad, without dorsal flap, conical,
tip almost straight, with distinct ventral
distal opening.

Broad, without subdistal cleft on outermargin, without distinct rounded distal
protuberance on outer margin.

Broad, about 2.8 times longer thanbroad, without dorsal flap, conical,
without distinct narrowing towards tip,very slightly curved, with large ventral
distal opening.

Slender, sinuous, without subdistal cleft
on outer margin, without protuberanceon outer margin.

Broad,'about 2.6 times longer thanbroad, without dorsal flap, subconical,
with distinct narrowing towards blunt
tip, with ventral distal opening.

Broad, with distinct subrectangularsubdistal cleft on outer margin, with
distinct rounded distal protuberance onouter margin.

Broad, about 2.3 times longer thanbroad, without dorsal flap, subconical,
with distinct narrowing towards acutetip, without ventral distal opening.

Broad, without subdistal cleft on outermargin, without distinct rounded distal
protuberance on outer margin.

Slender, about 3.2 times longer thanbroad, without dorsal flap, conical,
without distinct narrowing towards tip,with tip slightly curved downwards,
without ventral distal opening.

Broad, with distinct rectangular subdistal
cleft on outer margin, without distinct
rounded distal protuberance on outermargin.

Broad, about 2.6 - 2.8 times longer
than broad, without dorsal flap,
subconical, with distinct narrowing
towards blunt tip, with ventral distal
opening.

Broad, with weak subdistal cleft onouter margin, without distinct roundeddistal protuberance on outer margin.

segment

Broad, about 2.7 times longer than
Broad, with slight subdistal cleft on
broad, without dorsal flap, conical,
outer margin, without distinct rounded
gently tapering distally, without distinct distal protuberance on outer margin.
narrowing towards tip, with distinct
subdistal angle on upper margin, withslit-like ventral distal opening.
Broad, about 2.6 times longer than
Broad, without subdistal cleft on outerbroad, without dorsal flap, conical,
margin, without distinct rounded distal
gently tapering distally, without distinct protuberance on outer margin.
narrowing towards tip, almost straight,
upper margin smoothly, gently convex
and without subdistal angle, withslit-like ventral distal opening.

Potamon orleansi Rathbun, 1904
(Figs. 2H-L, 6B)
Potamon (Potamon) orleansi Rathbun, 1904: 282, Fig. 20, PI. 11 fig. 7.
Potamiscus (Potamiscus) tannanti - Batt 1966: 480, ?Fig. 14 (part)(not Potamon (Potamon) tannanti
Rathbun, 1904).
Potamiscus tannanti - Batt 1970: 160 (part); Dang 1975: 75, 1980: 432 (part)(not Potamon (Potamon)
tannanti Rathbun, 1904).
Material examined. - Holotype, male (42.4 by 32.3 mm) from "Tonkin, riviere Noire" (river Song
Da)(MNHN-B 5262) coll. Prince Henri d'Orleans, no date.

Diagnosis. - Carapace broader than long, low, dorsal relatively flat, surface glabrous; regions
not well-defined. Epigastric cristae distinct, not sharp, rugose; postorbital cristae relatively
sharp, breaking up into low, flat rugae just before epibranchial tooth; regions behind epigastricand postorbital cristae distinctly rugose. External orbital angle triangular, outer margin slightly
convex; epibranchial tooth low, triangular; anterolateral margin convex, weakly serrated,distinctly cristate; posterolateral margins not strongly convergent posteriorly; branchial region
weakly rugose. Ischium of third maxilliped rectangular. Carpus of chelipeds with anterior
part of outer margin entire. Suture between thoracic sternites 3 and 4 discernible only bynotches at lateral edges of sternum. Telson of male abdomen triangular, with lateral margins
distinctly concave. G 1 slender, sinuous; terminal segment about 0.3 times length ofsubterminal segment, broad, about 2.8 times longer than broad, without dorsal flap, conical,
tapering gently distally, not "bottle-neck"-Iike, without distinct narrowing towards tip, veryslightly curved, with gently concave lower margin, with upper margin distinctly convex
towards tip, with relatively broad distal part and tip, with large ventral distal opening;
subterminal segment slender, without neck-like distal part, sinuous, without subdistal cleft
on outer margin, without protuberance on outer margin. G2 missing but probably with distalsegment greater than half length of basal segment.
Remarks. - The sole specimen of Potamon orleansi, a male (MNHN-B 5262)(42.4 by 32.3mm), mentioned in the original description by Rathbun (1904) is, by default, the holotype
for the species. Although no date is written on the label, Henri Philippe Marie Duc d'Orleandmade natural history collections in Vietnam (formerly French Indochina) in 1890, 1891,
1895 and 1901, and the date of collection of the holotype is probably in one of these years(L. B. Holthuis, in litt.). It is unfortunately, in very poor condition, with the chelipeds andambulatory legs being badly broken. The G I, while retaining its original shape, has several
breakages on the subterminal segment. In addition, some of the important morphologicalfeatures are missing, including the exopods of the third maxillipeds, G2s and abdomen. The
information in the diagnosis on the tel son of the male abdomen is based on Rathbun's (1904:
Fig. 20) illustration of the distal abdominal segments of the male type specimen.
Bott (1966, 1970) synonymised Potamon orleansi under Potamiscus tannanti, but without
indicating whether the type specimens of either species had been examined. Dang (1975,1980) also regarded P. orleansi as a junior synonym of P. tannanti, in apparent agreementwith Bott' s (1966, 1970) work. Ng & Naiyanetr (1993: 20) also mentioned Bott' s action but
noted that" ... the differences in the carapace features of the two species (fide Rathbun, 1904)
suggest otherwise". In the present study, after reexamining the male holotype of P. orleansi
and comparing it with P. tannanti s. str., we have confirmed that the two are distinct species,differing in both carapace as well as G 1 characters (see Tables 1,2). The G I figured by Bott
(1966: Fig. 14) superficially resembles that of the P. orleansi holotype but Bott did notindicate which specimen was drawn. Thus, the specimen in his figure can only be tentatively
referred to P. orleansi.
The type locality of P. orleansi, "Tonkin, riviere Noire", is not very' precise as it refers to
the present day river Song Da in northern Vietnam, a major tributary of the Red River,which drains through Lai Chau as well as Son La provinces (The Times Atlas of the World,
9th Edition, Bartholomew and Times Books, 1992: PI. 25 H2). Two allied species, Potamon
jinpingense Dai, 1995, and P. mieni Dang, 1967, are reported from the two provinces
respectively (present study). Potamon orleansi is nevertheless easily distinguished fromthese species by its distinctive G 1 structure (present study)(see Table 2). Rathbun (1904)
noted the similarity of P. orleansi with Potamon luangprabangense
Rathbun, 1904. The

Fig. 2. A-G, Potamon tannanti Rathbun, 1904, A, holotype female (35.5 by 27.7 mm)(MNHN-B
5313), B-G, male (56.1 by 42.6 mm)(ZRC 1998.264); H-L, Potamon orleansi Rathbun, 1904, holotype
male (42.4 by 32.3 mm)(MNHN-B 5262). A, H: left third maxilliped; B, J: ventral view of left GI;
C, I: dorsal view of left G I; D: telson; E, K: dorsal view of terminal segment of left G I; F, L: ventral
view of terminal segment of left G I; G: left G2. Scales = 2.0 mm in A-D, G, I-J; 1.0 mm in E-F, KL; 5.0 mm in H.

two species resemble each other in carapace morphology, with their distinctly rugose regions
behind the epigastric and postorbital cristae, as well as in postorbital cristae which break up
into low, flat rugae just before epibranchial tooth (cf. Rathbun, 1904: PI. II fig. 9). We
have, however, examined the male type specimen of P. luangprabangense (47.8 by 35.5mm)(MNHN-B5225), and found that their G 1 structures clearly differ at the specific level(cf. Bott 1970: PI. 37 fig. 6). The type of P.luangprabangense examined is also the specimen
illustrated by Rathbun (1904: Fig. 19, PI. II fig. 9) and Bott (1970: 169, PI. 37 fig. 6, PI. 48
fig. 35), as evident by the damaged left external orbital angle. The G I of P. orleansi is,instead, most similar to Potamon villosum, new species (present study). The differences
between P. orleansi and P. villosum, new species, are documented under the Remarks forthe latter species (see later).

Potamon mieni Dang, 1967
(Figs. 3A-G, 6C)
Potamon (Potamon) luangprabangensis mieni Dang, 1967: 158, Fig. 5.
Potamiscus tannanti - Dang 1975: 75, 1980: 432 (part)(not Potamon (Potamon) tannanti Rathbun,
1904).

Material examined. - 1 male (57.1 by 43.5 mm), I juvenile female from Thuan Chau District, Son
La Province, northern Vietnam (ZRC 1998.265) coli. V. D. Nguyen, 1997.

Diagnosis. - Carapace broader than long, low, dorsal surface relatively flat, glabrous; regions
not well-defined. Epigastric cristae distinct, not sharp, rugose; postorbital cristae weakly
rugose, breaking up into granules and low rugae just before epibranchial tooth; regions behind
epigastric and postorbital cristae weakly rugose. External orbital angle triangular, outermargin slightly convex; epibranchial tooth low, triangular; anterolateral margin convex,
weakly serrated, distinctly cristate; posterolateral margins not strongly convergent posteriorly;
branchial region weakly rugose. Ischium of third maxiIliped rectangular. Carpus of chelipeds
with anterior part of outer margin entire. Suture between thoracic sternites 3 and 4 discernible
only by notches at lateral edges of sternum. Telson of male abdomen narrowly triangular,
with lateral margins distinctly concave. G 1 broad; terminal segment about 0.3 times lengthof subterminal segment, broad, about 2.6 times longer than broad, without dorsal flap,
subconical, "bottle-neck" -like, with distinct narrowing towards blunt tip, with ventral distal
opening; subterminal segment broad, without neck-like distal part, with distinct subrectangularsubdistal cleft on outer margin, with distinct rounded distal protuberance on outer margin.
G2 with distal segment greater than half length of basal segment.
Remarks. - Dang (1967) originally described Potamon mieni (as a subspecies of P.
luangprabangense), with simple and somewhat schematic illustrations of the frontal region,right third maxilliped, telson and right G 1, based on two male specimens, one of whichmeasured 56.0 by 43.0 mm. These syntypes were collected from Hoa Binh Province but noother information about the locality was given (Dang 1967), and we have not been able toexamine them. Despite this, the present specimens from Thuan Chau District in Son La
Province of northern Vietnam have been referred to P. mieni as Son La Province is adjacent(northwest) and upstream of Hoa Binh Province (part of the Song Da river drainage). The
types of P. mieni, originally deposited in the Zoological Museum of Hanoi University(ZMHU), may well be lost (N. T. Dang, in litt.). This situation resulted from the shifting

of ZMHU material to the jungle, and further shifting about within the jungle, during theVietnam War to avoid destruction by enemy bombing. The specimens in the ZMHU are
therefore, in considerable disorder (N. T. Dang, in Iitt.; pers. comm.). Even if the relevantlots are found, the deteriorated condition of the specimens and confusion within the mixed
lots may render the types indistinguishable from non-types. If the types of P. mieni areindeed lost, then one of the present specimens should be designated as a neotype and thepresent diagnosis of the species should apply to P. mieni.
Potamon mieni was synonymised under Potamiscus tannanti (Rathbun, 1904)[sensu Bott
1966, 1970], without stating what material was examined (see Dang 1975, 1980). It is highly
likely therefore, that much of the material resembling P. tannanti collected from northern
Vietnam since the 197Qs have been assigned to that species. This is the case with the present
specimens which wer~ originally identified as P. tannanti. They are, however, clearly not
P. tannanti as presently defined and differ in carapace, male telson and G I characters (seeTables I, 2). Potamon mieni most closely resembles Potamon guttus, new species, but canbe separated from it male tel son and G I characters (see Tables I, 2).

Distribution. - Thuan Chau District, Son La Province, northern Vietnam (present study);
Hoa Binh Province (Dang 1967).

Potamon jinpingense Dai, 1995
(Figs. 3H-O, 6D)
Potamon jinpingense Dai, 1995: 52, Fig. 4, PI. I figA.
Potamiscus tannanti - Dang 1975: 75, 1980: 432 (part)(not Potamon (Potamon) tannanti Rathbun,
1904).

Material examined. - 2 males (larger 64.0 by 47.0 mm) from Sin Ho District, Lai Chau Province,
northern Vietnam (ZRC 1998.266) call. V. D. Nguyen, Nov.1997.

Diagnosis. - Carapace broader than long, low, dorsal surface relatively t1at, glabrous; regions
not well-defined. Epigastric cristae distinct, not sharp, rugose; postorbital cristae weakly
rugose, breaking up into granules and low rugae just before epibranchial tooth; regions behind
epigastric and postorbital cristae weakly rugose. External orbital angle triangular, outermargin slightly convex to almost straight; epibranchial tooth triangular, low; anterolateral
margin convex, serrated, distinctly cristate; posterolateral margins not strongly convergent
posteriorly; branchial region weakly rugose. Ischium of third maxilliped rectangular. Carpus
of chelipeds with anterior part of outer margin entire. Suture between thoracic sternites 3
and 4 discernible only by notches at lateral edges of sternum. Telson of male abdomen
narrowly triangular, with lateral margins distinctly concave. G I broad; terminal segment
about 0.3 times length of subterminal segment, broad, about 2.3 times longer than broad,without dorsal t1ap, subconical, "bottle-neck"-like, with distinct narrowing towards acutetip, without ventral distal opening; subterminal segment broad, without neck-like distal part,without subdistal cleft on outer margin, without distinct rounded distal protuberance on outermargin. G2 with distal segment greater than half length of basal segment.

Remarks. - Several new species of freshwater crabs from several localities in and around themountains of the Sino-Vietnam border in Yunnan Province, China, were described by Dai(1995) and Dai et al. (1975). Two of these species, Potamon hokuoense Dai, Song, He, Cao,
Xu & Zhong, 1975, and P. jinpingense Dai, 1995, have been found to be conspecific with

Fig. 3. A-G, ?otamon mieni Dang, 1967, male (57.1 by 43.5 mm)(ZRC 1998.265); H-O, ?otamon
jinpingense Dai, 1995, H-J, L-O, male (64.0 by 47.0 mm)(ZRC 1998.266), K, male (54.5 by 40.7mm)(ZRC 1998.266). A, H: left third maxilliped; B, I: dorsal view of right G I; C, J-K: ventral viewof right G 1; 0, L: te1son; E, M: ventral view of terminal segment of right G1; F, 0: right G2; G, N:
dorsal view of terminal segment of right G 1. Scales = 5.0 mm in A, H; 2.0 mm in B-D, F, I-L, 0;
1.0 mm in E, G, M-N.

the northern Vietnamese species in this study. Potamon hokuoense has already been shown
to be conspecific with the holotype of P. tannanti Rathbun, 1904 (see earlier), while thepresent specimens are referred to P. jinpingense.
Like P. mieni (see earlier), the present specimens were also first identified as P. tannanti(Dang, unpublished).
They are, however, different species and the former is actuallyconspecific with P. jinpingense (present study), with the present specimens closely matching
the description and figures given by Dai (1995). Furthermore, the area from which thepresent specimens were collected from (Sin Ho District, Lai Chau Province, northern Vietnam)
is relatively near to (about 45 km) and downstream (tributaries of the Song Da river) fromthe type locality of P. jinpingense, Hetuozhai, Jinping, Yunnan Province, southern China.
Potamon jinpingense J~pears to be closest to P. mieni Dang, 1967, and P. guttus, new species.
It can, however, be distinguished from the latter two species by differences in the G I structure,and from other species in the present study by carapace and male telson characters (seeTables 1,2).
Allometric growth of the G I is illustrated here, which is commonly observed in potamid
crabs (Ttirkay & Naiyanetr, 1987: 391; unpublished data). The GI of the larger specimen
differs from that of the smaller specimen in its terminal segment being slightly more stout,
proportionately shorter with respect to the subterminal segment and more bent towards theperpendicular, while its subterminal segment is also more stout (cf. Figs. 3J, K). In someother unrelated species of potamid crabs, such as members of Demanietta Bott, 1966, andJohora Bott, 1966, this trend is reflected in a curved terminal segment becoming more strongly
curved in larger specimens (unpublished data).

Distribution. - Sin Ho District, Lai Chau Province, northern Vietnam (present study);
Hetuozhai, Jinping, Yunnan Province, southern China (Dai 1995).

Potamon cua, new species(Figs. 4A-G, 7A)
Patamiscus1904).

tannanti - Dang, 1975: 75, 1980: 432 (part)(not Pataman (Pataman) tannanti Rathbun,

Materml examined. - Holotype, male (46.9 by 36.6 mm)(ZRC 1998.267), Tam Dao, Vinh Phu Province,
northern Vietnam, coil. X. Q. Nguyen, 8 Jun. 1997 . Paratypes - 2 females (larger 42.6 by 33.0 mm),
2 juvenile males (ZRC 1998.268-271), same locality and collector as holotype, Mar. 1997 .

Diagnosis. - Carapace broader than long, low, dorsal surface relatively flat, very sparsely
setose in metabranchial region, with short, indistinct setae; regions well-defined, giving
strongly sculptured appearance. Epigastric cristae distinct, not sharp, rugose; postorbitalcristae sharp, weakly cristate, breaking up into granules and rugae just before epibranchial
tooth; regions behind epigastric and postorbital cristae weakly rugose to weakly granular.
External orbital angle triangular, outer margin almost straight; epibranchial tooth triangular,
low; anterolateral margin convex, weakly serrated, distinctly cristate; posterolateral margins
not strongly convergent posteriorly; branchial region distinctly rugose. Ischium of third
maxilliped rectangular. Carpus of chelipeds with anterior part of outer margin entire. Suture
between thoracic sternites 3 and 4 discernible only by notches at lateral edges of sternum.
Telson of male abdomen triangular, with lateral margins slightly concave. G 1 broad; terminalsegment about 0.4 times length of subterminal segment, slender, about 3.2 times longer thanbroad, without dorsal flap, conical, without distinct narrowing towards tip, with tip slightly
curved downwards, without ventral distal opening; subterminal segment broad, without necklike distal part, with distinct rectangular subdistal cleft on outer margin, without distinct
rounded distal protuberance on outer margin. G2 with distal segment greater than half lengthof basal segment.

Remarks. - Potamon cua, new species, is another member of the Potamon tannanti groupwhich has been confused with P. tannanti and the records of Potamiscus tannanti in northern
Vietnam probably include this species as well (see Dang 1975, 1980).
I'

Potamon cua is closest to P. tannanti in the proportions of the G 1, however, the actual shapeand morphology of the G I of the two species clearly distinguishes them from one another(see Table 2).

Potamon guttus, new species(Figs. 4H-R, 7B)
Potamiscus (Potamiscus) tannanti - Bott 1966: 480 (part)(not Potamon (Potamon) tannanti Rathbun,
1904).
Potamiscus tannanti - Bott 1970: 160, ?PI. 38 fig. 30 (part) (not Potamon (Potamon) tannanti Rathbun,
1904).

Material examined. - Holotype, male (62.2 by 45.7 mm)(ZRC 1998.272), Ban Long Cheng, Muang
Saisombun, Saisombun Special Zone, northern Laos, coil. Viroj Kittikoon, May.1995. Paratypes - 1
male (43.8 by 34.7 mm)(ZRC 1998.273), same data as holotype. 2 males (larger 60.2 by 46.3)(CUMZ),
same data as holotype. I female (33.1 by 25.3 mm)(ZRC 1998.274), side of dam, Muang Saisombun,
Saisombun Special Zone, northern Laos, coil. Viroj Kittikoon, May 1995. Others - 8 specimens (largest
male 51.3 by 38.8 mm)(MNHN-B 5316) "Haut Laos, Ban Nong", coil. Mission Permanente, 10
Jan.1906.

Diagnosis. - Carapace broader than long, low, dorsal surface relatively flat, glabrous; regions
well-defined, giving strongly sculptured appearance. Epigastric cristae distinct, not sharp,
rugose; postorbital cristae sharp, gently cristate, breaking up into granules and rugae justbefore epibranchial tooth; regions behind epigastric and postorbital cristae weakly rugose to
weakly granular. External orbital angle triangular, outer margin almost straight; epibranchial
tooth acute, low; anterolateral margin convex, distinctly serrated, distinctly cristate;
posterolateral margins not strongly convergent posteriorly; branchial region distinctly rugose.
Ischium of third maxilliped rectangular. Carpus of chelipeds with anterior part of outermargin entire. Suture between thoracic sternites 3 and 4 discernible only by notches at lateraledges of sternum. Telson of male abdomen triangular, with lateral margins slightly concave.
G 1 broad; terminal segment about 0.3 times length of subterminal segment, broad, about 2.6- 2.8 times longer than broad, without dorsal flap, subconical, "bottle-neck"-like, with distinct
narrowing towards blunt tip, with ventral distal opening; subterminal segment broad, without
neck-like distal part, with weak subdistal cleft on outer margin, without distinct roundeddistal protuberance on outer margin. G2 with distal segment greater than half length of basal
segment.

Fig. 4. A-G, Potamon cua, new species, holotype male (46.9 by 36.6 mm)(ZRC 1998.267); H-R,
Potamol1 guttus, new species, H, K-L, N-Q, halo type male (62.2 by 45.7 mm)(ZRC 1998.272), I,
paratype male (43.8 by 34.7 mm)(ZRC 1998.273), J, paratype female (33.1 by 25.3 mm)(ZRC
1998.274), R, male (51.3 by 38.8 mm)(MNHN-B 5316). A, H: left third maxilliped; B, K: dorsal viewof right G I; C, L-M: ventral view of right G I; D, 0: telson; E, Q: ventral view of terminal segmentof right G I; F, N: right G2; G, P: dorsal view of terminal segment of right G I; I, J: distal part of left
third maxilliped exopod; R: ventral view of left G I. Scales = 5.0 mm in A, H; 2.0 mm in B-D, F, 1R; 1.0 mm in E, G.

Etymology. - The specific epithet, guttus, is Latin for "narrow-necked
the G I terminal segment shape. Used as a noun in apposition.

flask" in allusion to

Remarks. - Potamon guttus, new species, is closest to P. jinpingense and P. mieni by virtue
ofthe subconical G I terminal segment which is distinctly "bottle-neck" -like, with a narrowing
towards tip. Potamon guttus can, however, be distinguished from the latter two species byslight but consistent differences in the G I (see Table 2).
It should be noted that the flagellum of the right third maxilliped exopod of the holotype isvery short, probably due to regrowth following earlier damage. However, the intact left
third maxilliped exopod flagellum is similar to the other species covered in this study, being
well-developed but not exceeding the width of the merus. The male paratype has rounded,vestigial flagella on bo\h third maxillipeds, while the female paratype has very short, roundedflagella on both third maxillipeds (cf. Figs. 41, J). These flagella do not appear to be broken
or damaged as the tips are neither straight nor jagged, in which case, this would be an example
of variation, with flagellum length slowly increasing with size and age. It is also possiblethat the third maxilliped flagella of both paratypes had been pulled out and rounded stumps
represent a regrowth.
Like the previous species, size- or age-related variation in G I
morphology is also evident for P. guttus (cf. Figs. 4L, M).
Bott (1966, 1970) had included three males and one female juvenile from "Ban-Nong, Ober
Laos", in the material examined under Potamiscus tannanti. We have examined eightspecimens (MNHN-B 5316) from this lot and found them not to be conspecific with P.
tannanti s. str., differing slightly in carapace morphology but considerably in G I form (cf.
Fig. 4R). These specimens are almost identical to the type material of P. guttus and havetherefore been assigned to this species. However, the precise location of the "Ban-Nong,Ober Laos" from which the specimens were collected remains doubtful. We have foundthree such places in Laos, one Ban Nong in Luang Prabang Province [northern Laos], about
100 km to the north of the type locality, one in Sainyabuli Province [northern Laos], about
200 km to the southwest, and one in Bolikhamsai Province [northern-central Laos], morethan 250 km to the southeast. In all three cases, the drainage for that area is not connectedto that of the type locality of P. guttus at all. In any case, there is also no assurance that anyof these places might be the original "Ban-Nong".
The photograph of a G 1 of "P. tannanti" by Bott (1970: PI. 38 fig. 30) has no other information
about the specimen and we cannot be sure which one of the specimens examined by Bott
(1966) was photographed.
It most closely resembles the G I of P. guttus in possessing abroad terminal segment with distinct narrowing towards a blunt tip and a subterminal segmentwith a weak subdistal cleft on the outer margin, and the specimen in question is tentatively
referred to this species.
Distribution. - Ban Long Cheng, Muang Saisombun, Saisombun Special Zone, northern
Laos (present study); "Haut Laos, Ban Nong" (Bott 1966)(?).

Potamon ou, new species(Figs. 5A-G, 7C)
Material examined. - Holotype, male (35.6 by 27.1 mm)(ZRC 1998.275), Nam Ou at confluencewith Huay Nam, 21 °4' 10"N 102 31' 44"E, 3 km ESE of Muang Khoa, Phongsali Province, northern
Laos, coil. M. Kottelat, 17 May.1997.
0

Diagnosis. - Carapace broader than long, low, dorsal surface relatively flat, glabrous; regions
not well-defined. Epigastric cristae distinct, not sharp, rugose; postorbital cristae not sharp,
rugose, breaking up into granules and rugae just before epibranchial tooth; regions behind
epigastric and postorbital cristae rugose. External orbital angle triangular, outer margin
slightly convex to almost straight; epibranchial tooth triangular, low; anterolateral margin
convex, distinctly serrated, strongly cristate; posterolateral margins not strongly convergent
posteriorly; branchial region rugose. Ischium of third maxilliped rectangular. Carpus ofchelipeds with anterior part of outer margin entire. Suture between thoracic sternites 3 and4 discernible only by notches at lateral edges of sternum. Telson of male abdomen narrowly
triangular, with lateral margins distinctly concave. G I broad; terminal segment about 0.3
times length of subterminal segment, slender, about 2.7 times longer than broad, without
dorsal flap, conical, geptly tapering distally, not "bottle-neck" -like, without distinct narrowing
towards tip, almost straight, lower margin straight towards tip, upper margin straight with
distinct subdistal angle towards tip, with slit-like ventral distal opening; subterminal segment
broad, without neck-like distal part, with slight subdistal cleft on outer margin, without distinct
rounded distal protuberance on outer margin. G2 with distal segment greater than half lengthof basal segment.
Etymology.
apposition.

- This species is named after its type locality, Nam au.

Used as a noun inRemarks. - The form of its G 1 most closely allies Potamon ou, new species, with Potamon
villosum, new species. Indeed, the holotype of P. ou was obtained from a province (Phongsali)adjacent to the province (Luang Nam Tha) where Potamon villosum was collected. The
terminal segment of the G I of P. ou, however, clearly differs from that of P. villosum inbeing more slender and having a straight upper margin with a distinct subdistal angle towards
the tip (versus more robust and upper margin smoothly, gently convex towards tip, without
subdistal angle). In addition, P. ou has a glabrous dorsal carapace while P. villosum has asetose dorsal carapace (see Table I).

Potamon villosum, new species(Figs. SH-O, 7D)
Material examined. - Holotype, male (44.8 by 34.3 mm)(ZRC 1998.276), Tributaries of Nam Tha
River ca. 800 mas!., Luang Nam Tha Province, northern Laos, coIl. H. Morioka, 13 Nov.1997.
Paratypes. - 7 males (largest 55.9 by 41.4 mm), 4 females, 1 juvenile (ZRC 1998.277-285,807-809),
same data as holotype. 2 females (larger 32.9 by 24.5 mm)(ZRC 1998.286-287) from Nam Luang ca.
t km upstream of Ban Nam Luang, Nam Tha watershed, Mekong basin, Luang Nam Tha Province,
northern Laos, 21 9'5" N 101 20'34" E, coIl. M. Kottelat, 22 May 1997. 1 female (39.9 by 30.8mm)(ZRC 1998.288), tributary ofNam Talan ca. 3 km S of Ban Nateuy, Nam Tha watershed, Mekongbasin, Luang Nam Tha Province, northern Laos, coli. M. Kottelat, 20 May 1997.
00

Diagnosis. - Carapace broader than long, low, dorsal surface relatively flat, distinctly setose,
especially in metabranchial region; regions not well-defined. Epigastric cristae distinct, notsharp, rugose; postorbital cristae not sharp, rugose, breaking up into strong granules andrugae just before epibranchial tooth; regions behind epigastric and postorbital cristae strongly
rugose. External orbital angle triangular, outer margin slightly convex to almost straight;
epibranchial tooth triangular, low; anterolateral margin convex, distinctly serrated, strongly

:;;

~~:

H

Fig. 5. A-G, Potamon ou, new species, holotype male (35.6 by 27.1 mm); H-O, Potamon villosum,
new species, H-J, L-O, holotype male (44.8 by 34.3 mm)(ZRC 1998.276), K, paratype male (32.8 by
25.4 mm)(ZRC 1998.277); A, H: left third maxilliped; B, 1: dorsal view of right G 1; C, J, K: ventral
view of right G 1; D, L: telson; E, M: ventral view of terminal segment of right G 1; F, 0: right G2;
G, N: dorsal view of terminal segment of right G 1. Scales = 2.0 mm in A-D, F, H-L, 0; 1.0 mm in
E-G, M-N.

cristate; posterolateral margins not strongly convergent posteriorly; branchial region distinctly
rugose. Ischium of third maxilliped rectangular. Carpus of chelipeds with anterior part ofouter margin entire. Suture between thoracic sternites 3 and 4 discernible only by notchesat lateral edges of sternum. Telson of male abdomen narrowly triangular, with lateral margins
distinctly concave. 01 broad; terminal segment about 0.3 times length of subterminal
segment, broad, about 2.6 times longer than broad, without dorsal flap, conical, gently tapering
distally, not "bottle-neck"-like, without distinct narrowing towards tip, almost straight, withstraight lower margin and upper margin smoothly, gently convex towards tip, with slit-likeventral distal opening; subterminal segment broad, without neck-like distal part, without
subdistal cleft on outer margin, without distinct rounded distal protuberance on outer margin.
02 with distal segment gre~ter than half length of basal segment.
Etymology. - The spebific epithet is derived from villosus, Latin for hairy, alluding to thesetose carapace.
Remarks. - Potamon villosum, new species, is closest to P. ou, new species, and their main
distinguishing characters have already been mentioned under the Remarks for the latter species(see earlier). The broad 01 terminal segment of P. villosum, also allies it with P. jinpingense,
P. mieni, and P. guttus. It is, however, easily separated from these as well as the otherspecies covered in the present study by its distinctly setose carapace (versus glabrous tovery sparsely setose)(see Table 1). It is interesting to note that the short, stiff, black setae
are not velvety and not easily scraped off; being deeply inserted into the carapace in deep,
well-defined pits, which are visible even after the setae are removed.
Potamon villosum also superficiallyresembles Potamon hispidum (Wood-Mason,
187l)[Upper Burma]. However, the anterolateral margins of P. villosum appear to be more
distinctly convex, giving its carapace a more transverse appearance (versus less strongly
convex anterolateral margins, giving appearance of squarish carapace in P. hispidum). In
addition, the very sparsely setose ambulatory legs of P. villosum immediately distinguish itfrom P. hispidum, which was described by Wood-Mason (1871: 452) as having ridges ofambulatory leg joints being "thickly covered with bundles of hairs" and by Alcock (1910:36) as being "thickly beset with tufts of stiff bristles".

Material examined. - 2 females (larger 55.6 by 41.3 mm)(ZRC 1998.289), Nam Phao at waterfall
immediately
downstream of border post on road from Lak Sao to Vietnam(ca. l8°23'OO"N
105°09'20"E), Bolikhamsai Province, central Laos, colI. M. Kottelat, 19 Mar. 1996.

Remarks. - The present specimens externally resemble a number of the species in the present
paper, viz., Potamon tannanti, P. mieni, P. jinpingense, P. cua, P. guttus and P. ou, but are
unusual in that the anterolateral margin cristae are large and further apart than in other species.
Unfortunately, no male specimens were collected from that locality and so the 01 of thisspecies are not available for examination. They are thus regarded as incertae sedis andassigned to Potamon sp. until fully mature male specimens can be obtained from the same
locality in order to examine the diagnostically important 01s.

Fig. 6. A, Potamon tannanti Rathbun, 1904, holotype female (35.5 by 27.7 mm)(MNHN-B 5313); B, Potamon orleansi Rathbun, 1904, holotype
male (42.4 by 32.3 mm)(MNHN-B 5262); C, Potamon mieni Dang, 1967, male (57.1 by 43.5 mm)(ZRC 1998.265); D, Potamonjinpingense
Dai, 1995, male (64.0 by 47.0 mm)(ZRC 1998.266).

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Fig. 7. A, Potamon cua, new species, holotype male (46.9 by 36.6 mm)(ZRC 1998.267); B, Potamon guttus, new species, holotype male (62.2 by
45.7 mm)(ZRC 1998.272); C, Potamon ou, new species, holotype male (35.6 by 27.1 mm); 0, Potamon villosum, new species, holotype male (44.8
by 34.3 mm)(ZRC 1998.276).

KEY TO POTAMON TANNANTI SPECIES GROUPFROM NORTHERN INDOCHINA
1. G I terminal segment slender (ca. 3.2 - 3.6 times longer than broad)G I terminal segment broad (ca. 2.3 - 2.8 times longer than broad)

2
3

2.

Epigastric region granulose to very weakly rugose. Sixth segment of male abdomen with distinctly
convex lateral margins.
GI subterminal segment without subdistal cleft on outer margin;terminal segment with tip almost straight (Figs. lA, C, 2B-C, E-F, 6A) [northern Vietnam,
southern China]
P. tannanti Rathbun, 1904
Epigastric region distinctly rugose. Sixth segment of male abdomen with slightly convex lateral
margins. G I subterminal segment with distinct rectangular subdistal cleft on outer margin;terminal segment with tip slightly curved downwards (Figs. 4B-C, E, G, 7A) [northern Vietnam].........................
IL
P. cua, new species

3.

G I terminal segment conical, tapering gently distally, not "bottle-neck"-like,
without distinct
narrowing towards tip
4
GI terminal segment subconical, "bottle-neck"-like,with distinct narrowing towards tip
64.

Anterolateral margin weakly serrated; branchial region weakly rugose. G I subterminal segment
slender, sinuous; terminal segment very slightly curved (Figs. 2I-L, 6B) [northern Vietnam].........................................................................................................
P. orleansi Rathbun, 1904
Anterolateral
margin distinctly serrated; branchial region rugose to distinctly rugose. G I
subterminal segment broad, gently sinuous; terminal segment straight..
55.

Dorsal carapace glabrous. G I terminal segment relatively more slender; upper margin straight,
with distinct subdistal angle towards the tip (Figs. 5B-C, E, G, 7C) [northern Laos].
......................................................................................................................
P. ou, new species
Dorsal carapace distinctly setose. G I terminal segment relatively more robust, upper marginsmoothly, gently convex towards tip, without subdistal angle (Figs. 5I-K, M-N, 7D) [northern
Laos]P. villosum, new species

6.

G I subterminal segment without subdistal cleft on outer margin; terminal segment tip acute, without
ventral distal opening (Figs. 3I-K, M-N) [northern Vietnam, southern China].
............................................................................................................
P. jinpingense Dai, 1995
G I subterminal segment with weak to distinct subdistal cleft on outer margin; terminal segment
tip blunt, with ventral distal opening
7

7.

Telson of male abdomen narrowly triangular, with distinctly concave lateral margins. G I
subterminal segment with distinct subrectangular subdistal cleft on outer margin, with distinct
rounded distal protuberance on outer margin (Figs. 3B-D, G) [northern Vietnam].
..................................................................................................................
.P. mieni Dang, 1967
Telson of male abdomen triangular, with slightly concave lateral margins. G I subterminal segmentwith weak subdistal cleft on outer margin, without distinct rounded distal protuberance onouter margin (Figs. 3I-N) [northern Laos]
P. guttus, new species

We are grateful to N. T. Dang (Vietnam National Centre for Natural Science and Technology)
and X. Q. Nguyen (National University of Hanoi) for graciously hosting us during our visit
to Hanoi; L. B. Holthuis for his useful comments; D. Guinot (MNHN); and C. M. Yang
(ZRC) for their help and access to material under their care. Some material used in this study
was generously contributed by H. Morioka (National Science Museum, Tokyo); M. Kottelat;
P. Naiyanetr (CUMZ); V. D. Nguyen (Institute of Malariology, Parasitology & Entomology,
Hanoi); and A. Y. Dai (Academia Sinica Beijing). Thanks also to H. K. Yip for his kind help
in developing the prints. This study is partially supported by research grant RP950326 tothe second author from the National University of Singapore, and is contribution no. 98/15
from the Systematics and Ecology Laboratory, Department of Biological Sciences, The
National University of Singapore.

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